1. Field of the Invention
The present invention relates to an ESD protection device and a composite electronic component thereof, and in particular, to an ESD protection device which is useful in a high-speed transmission system and, which can advantageously be combined with a common mode filter.
2. Description of the Related Art
In recent years, size reduction and performance improvement of electronic apparatuses have been rapidly in progress. Furthermore, much effort has been made to increase transmission speed (an increased frequency exceeding 1 GHz) and to reduce driving voltage as typically seen in high-speed transmission systems such as USB2.0, S-ATA2, and HDMI. On the other hand, the withstand voltage of electronic components used in electronic apparatuses decreases consistently with the size reduction of electronic apparatuses and the reduced driving voltage therefore. Thus, it has been important to protect electronic components from overvoltage typified by electrostatic pulses generated when a human body comes into contact with a terminal of an electronic apparatus.
In order to protect electronic components from such electrostatic pulses, a method of providing a banister or the like between the ground and a line to be subjected to static electricity has generally been used, and a method of adopting a surge absorber including long-lasting electrodes has been proposed (see Patent Documents 1 to 3). However, the use, in a high-speed transmission system, of the barrister or the like, which has a large electrostatic capacitance, not only increases a discharge starting voltage but also degrades signal quality.
On the other hand, an antistatic component with a low electrostatic capacitance has been proposed which includes an electrostatic protection material filled between opposite electrodes. For example, Patent Document 4 discloses an electric circuit protecting device (antistatic component) including a voltage varying polymer material disposed between electrodes, by applying a polymer material containing conductive particles into the gap area between the electrodes by stencil printing and thermally treating and solidifying the polymer material. Furthermore, Patent Document 5 discloses an antistatic component including an electrostatic protection material layer formed between a pair of electrodes by, in order to enhance an electrostatic inhibition effect, kneading metal particles with a passive layer formed on the surface thereof, a silicone-containing resin, and an organic solvent to obtain electrostatic protection material paste and applying the electrostatic protection material paste to between the opposite electrodes by screen printing before drying. Moreover, Patent Document 6 discloses an electric circuit protecting device (antistatic component) including a voltage dependent resistor layer composed mainly of zinc oxide and formed by providing ceramic paste containing metal oxide, a resin component, and a solvent component, subjecting the ceramic paste to screen printing so as to fill the gap between electrode paste films, and burning the ceramic paste at a high temperature.    [Patent Document 1] Japanese Patent Laid-Open No. 2007-242404    [Patent Document 2] Japanese Patent Laid-Open No. 2002-015831    [Patent Document 3] Japanese Patent Laid-Open No. 2007-048759    [Patent Document 4] National Publication of International Patent Application No. 2002-538601    [Patent Document 5] Japanese Patent Laid-Open No. 2007-265713    [Patent Document 6] Japanese Patent Laid-Open No. 2004-006594
However, the antistatic components described in Patent Documents 4-6 still provide high discharge starting voltages and fail to offer sufficient electrostatic absorption characteristics. Moreover, in the antistatic components described in Patent Documents 4-6, if any electrode is damaged during discharge, the electrodes may be short-circuited or the gap distance between the electrodes may vary, resulting in a significant variation in discharge starting voltage. Thus, these antistatic components cannot withstand repeated use.
The present invention has been made in view of the above circumstances. An object of the present invention is to provide an ESD protection device having a low discharge starting voltage and offering improved durability against repeated use, and a composite electronic component combined with the ESD protection device. Another object of the present invention is to provide an ESD protection device having excellent heat resistance and weather resistance, and allowing a further reduction in the thickness thereof, improvement of productivity, and a reduction in costs and a composite electronic component combined with the ESD protection device.